Conventional self-cleaning litter receptacles usually are open-top boxes that hold granular litter. Some litter boxes automatically remove animal waste from the litter, typically by using a motor to drive a sifting structure, such as a rake or scoop, through the litter to separate the waste from the litter. The motor must provide enough power to overcome the weight and agglomeration (i.e., adherence between litter grains) of the litter to push the rake through the litter, especially when starting the motion of the rake.
Prior self-cleaning litter receptacles can also take the form of a drum or other enclosure that holds the litter. For instance, U.S. Pat. No. 5,048,464, issued to Shirley, and U.S. Pat. No. 6,286,457, issued to Sugahara, both disclose a litter box with a motor that drives a drum for rotation that, in turn, rotates a helical-shaped screen or spiral filter attached to the sides of the drum for sifting through the litter. Use of a drum is advantageous because the drum keeps litter from escaping the litter box while it is rotating, and minimizes the unpleasant odors that emanate from typical open-top litter boxes. A rotating drum or cylinder, however, increases the power requirements of the motor because the motor is required to power the entire weight of the drum or other bulky enclosure for rotation as well as having to overcome the weight of the litter and waste contained therein.
Since the motor can be the most expensive component in the entire system, a self-cleaning litter receptacle that minimizes the power requirements of the motor while still sufficiently separating the animal waste from the litter would be desirable.